The authors describe a case of Marshall-Smith's syndrome in which there was a facial dysmorphic syndrome and considerable acceleration of bone maturation (24 months to 15 days). The infant had chronic respiratory distress and the aetiology of this condition is discussed, one possibility being a pneumopathy from repeated deglutition provoked by the micro-retrognathism. Hormonal investigations were normal. Contrary to the data in the first published reports, there was a pathological increase in size, as noted in subsequent observations by Weaver. Differential diagnosis is discussed in relation to patients with non-endocrine constitutional bony diseases. The cause of this syndrome is unknown.